The interrogation of detainees at Guantanamo Bay has saved Britain from at least two major terrorist attacks, according to President George Bush's chief intelligence adviser.

John Negroponte, Director of National Intelligence, claims information obtained from inmates at the camp has proved vital in thwarting a series of terror attacks around the world, including in Britain. But the claim has provoked anger among human rights groups, which argue it is being used to justify a number of practices at Guantanamo that may constitute torture.

Mounting calls for Guantanamo to be shut down amid fears it is breaching international laws on human rights has prompted Negroponte's office to take the unusual step of publicly defending the controversial camp in Cuba.

A summary of the so-called 'High-Value Terrorist Detainee Program', states that 'reporting from terrorist detainees has become a crucial pillar of US counterterrorism efforts, representing the single largest source of insight into al-Qaeda for the US and its CT (counter-terrorism) partners. The detention of terrorists disrupts - at least temporarily - the plots they were involved in, saving the lives not only of Americans, but also of countless men, women and children around the globe.'

It identifies two key terror plots in Britain that it says were disrupted thanks to information provided by detainees. 'In mid-2004, the US and its counterterrorism partners disrupted a plot that involved attacking urban targets in the United Kingdom with explosive devices. Some of the key leads to these plotters came from detainees.'

It also states that a 2003 plot to attack Heathrow airport using hijacked airliners was disrupted thanks to information from detainees. Other countries have apparently benefited too. The document states: 'In the spring of 2003, the US and a partner detained key al-Qaeda operatives who were in the advanced stages of plotting an attack against several targets in Karachi, Pakistan, that would have killed hundreds of innocent men, women and children.'

In all, the agency believes detainees have provided the names of 86 al-Qaeda operatives that are or have been 'deemed suitable for Western operations'.

Last night, Amnesty International reacted angrily to the claims, saying it ignored allegations that detainees had been placed in stress positions, subjected to sleep deprivation and submitted to 'water-boarding' - partial drowning.

'What is most worrying about the CIA assessment is its blatant disregard for basic human rights principles,' said Tim Hancock, Amnesty's UK campaigns director, who has studied the document.

'There is no sense that detained people are able to challenge the lawfulness of their detention or that they will ever face a proper trial.'

The decision by Bush's chief security adviser to link Guantanamo to a series of thwarted terror plots suggests that the US is concerned that even its closest political allies are turning against the camp. Lord Goldsmith, the Attorney General, and Lord Falconer, the Lord Chancellor, recently joined a growing list of politicians who have called for Guantanamo's closure.